Arthropod-borne flaviviruses, and especially dengue viruses, cause a wide range of important human diseases for which there are no specific therapies. To address this critical shortfall in preparedness to confront these emerging and re-emerging viruses we have established a program to investigate host factors as targets of anti-dengue therapy. We have discovered many novel drug targets using functional genomics and en masse biochemical approaches. Among these are the 3'-5' exonucleases of the DnaQ/DEDDh superfamily of enzymes: EXD2, WRN and ERI3 (PRNPIP)). These enzymes are highly related to virally encoded exonucleases in SARS coronavirus and Lassa fever virus suggesting that the DnaQ/DEDDh superfamily of enzymes is widely used by pathogenic viruses and thus inhibitors of these enzymes could have broad spectrum of activity. We propose to characterize these enzymes in detail and to identify compounds that inhibit their activity and dengue infection. This will be achieved by 1) Developing in vitro assays for EXD2, WRN and ERI3 and 2) developing in vivo (yeast-based) assays to screen inhibitors of EXD2, WRN and ERI3. Significance to public health. Flaviviruses, and especially dengue virus, are an emerging threat to public health in the US, a current risk to our armed forces and other citizens deployed around the world, and a major problem globally. At this time there is little that can be done to prevent or treat the majority of flaviviral infections and therefore development of anti-flaviviral drugs is of crucial importance.